This invention relates to a method and apparatus for machining a metal knuckle casting to meet dimensional and profile requirements for use in a standard AAR railroad coupler. More particularly, the present invention relates to such a method and apparatus to eliminate the inaccurate, laborious and time-consuming chipping and hand-grinding operations heretofore required for as-cast knuckle castings.
As is known in the art, railroad couplers used with rolling stock to carry freight, are made up of an assembly of parts, most of which are castings. The rough castings removed from the molds must be suitably cleaned and undergo some manual finishing operations to meet standards by the Association of American Railroads (AAR) for use in car couplers for freight service. The parts forming Type E, Type E/F and Type F AAR freight couplers all include coupler knuckles which have substantially the same configurations, although Type F knuckles are not identical to Type E knuckles. The couplers of the various types have other well-known distinctive differences. The coupler knuckles generally comprise a forward nose and a rearward tail containing a locking face. A pivot pin hole in the central knuckle body receives a pin member which is engaged by pivot lugs projecting outwardly from the knuckle side of a coupler head so that the nose portion of the knuckle can pivot away from and toward a front face in the coupler head. The nose portion of the knuckle swings towards the front face of the coupler head to the locked position when engaging with the nose portion of a knuckle of a mating coupler when the couplers are coupled together. Under pull, pulling faces on the nose portions of the locked knuckles engage each other. At the same time, a gap will exist between front face portions of the locked knuckles and the front faces of the mating couplers. This space generally determines the amount of slack in the couplers' 10-A contour areas between pull and buff.
Both the contour and the dimensions of the nose portion of the knuckle as well as the tail portion must meet AAR standard gage requirements. Any fins and lumps must be removed from the exterior areas of the pin hole hubs and it is usually necessary to hand-grind portions of the outer peripheral area of the knuckle casting to meet gaging requirements. Usually a portable grinder is directed by a workman along a path to smooth and remove surface imperfections from the knuckle casting. Subsequent inspection and gaging of the knuckle casting are carried out to assure suitability of the semi-finished casting. A protruding fin or parting line is generally present on the casting because of incomplete contact between the mating surfaces on the cope and drag halves of the mold. The fin or parting line extends along a peripheral surface of the casting forming one predominant area that requires extensive hand-grinding operations. The knuckle is generally symmetrical about the mold parting line. The opening in the casting to receive pivot pin extends perpendicular to the plane of the mold parting line. The hand-grinding operations are usually required across the front face of the knuckle casting from the nose portion thereof to a curved heel portion and thence to the outer surface of the hubs. From the surface of the hubs rearwardly, the hand-ground area extends to a tail stop that is the generally rearward extremity of the casting and intersects at a generally right-angle relation with a tail surface.
Grinding of these surfaces is achieved by the method and apparatus of the present invention to provide the required clearances of a proper fit within the coupler body and other parts for reliable operation of the coupler. Fitting of the knuckle with proper clearances between the rear of the knuckle tail and the front of a lock face of a lock in the coupler is very important for the lock set, knuckle throw and lock drop functions of the coupler. A clearance is necessary for dropping of the lock to the locked position. This requires grinding of the knuckle casting at the rear of the tail, the tail stop, the vertical area of the hub wall, areas between the tail stop and the hub for fit within the coupler body. Grinding of other knuckle areas must be carried out to assure proper engagement with a mating coupler and its knuckle. This includes grinding to a required knuckle contour for a proper fit in areas between the knuckle and the coupler front face, the knuckle nose and the body guard arm as well as throat faces of both of the couplers. AAR standards specify grinding to a " 10-A" contour to assure that the knuckle heel, the front face and the nose portion of the knuckle always have adequate clearance when joining with a mating coupler and its knuckle and for hinge movement of the mating coupler for proper tracking about horizontal track curves. It is neither necessary nor desirable to undertake extensive machining operations and incur the cost to machine all surfaces on the knuckle casting.